1. Field of the Invention
The invention relates to heat exchanger devices for cooling fluids used in an internal combustion engine, and more particularly, to a heat exchanger package including a coupled radiator and charge air cooler for an engine of a motor vehicle such as a heavy-duty highway truck or bus.
2. Description of Related Art
Heat exchanger packages comprising a radiator and a charge air cooler (CAC), also known as an intercooler, have been used for years in over the road highway trucks and buses and other heavy-duty motor vehicles. The radiator provides cooling for the engine coolant, usually a 50-50 solution of water and anti-freeze. The charge air cooler receives compressed, charge or intake air from the turbo- or super-charger and lowers its temperature before it enters the engine intake manifold, thereby making it denser, improving combustion, raising power output, improving fuel economy and reducing emissions. In order to optimize heat transfer in a given heat exchanger package size, the factors of cooling air flow, heat exchanger core restriction, cooling air flow split and cooling air approach and differential temperature must be balanced.
Numerous configurations of the radiator/charge air cooler heat exchanger package have been disclosed in the prior art. Placing both the radiator and charge air cooler side-by-side or vertically (as in U.S. Pat. No. 4,736,727), so that the full frontal area of each of the cores are exposed to ambient cooling air, provides the best performance, but requires the largest package frontal area. Limitations in the frontal area of radiator and charge-air cooler heat exchanger packages have been sought in order to accommodate the smaller frontal area of motor vehicles, as a result of improved vehicle aerodynamics. Heat exchanger packages with smaller frontal areas have been disclosed for example in U.S. Pat. Nos. 5,046,550, 5,316,079, 6,619,379 and 6,634,418, and in U.S. patent application Ser. No.10/289,513.
In another prior art radiator and charge air cooler heat exchanger package, depicted in FIG. 1, the charge air cooler is split between an upper unit 101 and a lower unit 103, disposed respectively behind and in front of radiator 107 with respect to the direction of cooling air flow 127. Radiator 107 has a conventional downflow-type tube and fin core 117 between upper tank 109a and lower tank 109b. Radiator 107 receives coolant 131 from the engine into upper tank 109a and the cooled engine coolant exits as 133 from the lower portion of lower tank 109b, to be transferred back to the engine. Both charge air cooler units 101, 103 are cross-flow type charge air coolers wherein the compressed charge air is flowed horizontally through the respective tube and fin cores 111, 113. Compressed, heated charge air 121 is first flowed into vertically oriented tank 105a of upper charge air cooler 101, through core 111 in direction 129a, and into vertical tank 105b. In unit 101, the charge air is cooled by air 127 as it exits the upper portion of radiator core 117. Thereafter, the partially cooled compressed charge air 123 is then transferred into vertical tank 105d of lower charge air cooler 103, where it is then flowed in horizontal direction 129b through core 113 and into vertical tank 105c, and thereafter exits 125 and flows to the engine intake manifold. In unit 103, the charge air is cooled by air 127 before it flows through the lower portion of radiator core 117. Notwithstanding its novel design, the heat exchanger package of FIG. 1 did not achieve good performance and did not go into normal production, to the inventor's knowledge. It has now been determined that the performance of the heat exchanger package of FIG. 1 suffered in large part due to excessive charge air pressure drop through the two charge air cooler units.
There is urgent need for greater engine cooling capacity in the highway trucks of the near future. One factor is the enactment of more stringent emission regulations which will become effective in 2007. Many engine manufacturers plan to meet the new requirements by means of exhaust gas recirculation (EGR), in which a portion of the engine exhaust gas is recirculated to the intake manifold for reburning. In this method, exhaust gas coolers are used to lower the temperature of the exhaust gas before it enters the intake manifold. The heat load from these coolers is added to the normal engine cooling heat load, requiring increased cooling capacity from the engine cooling system. The second factor is the demand by truck owners and operators for increased horsepower output in new trucks. Higher power output can contribute to higher average speeds over hilly terrain, shortening trip times and increasing profits. However, higher power output requires increased cooling capacity.
This need for increased cooling capacity poses a dilemma for truck builders that have recently invested heavily in aerodynamic styling for their trucks. The sloping hoods of new trucks seen on the highway today are a result of this restyling, which places extreme limitations on the size of the engine cooling package. At the present time, truck manufacturers are seeking a solution to the problem of providing increased cooling capacity without costly redesign of the truck front end, which includes the hood, grille, bumper and fenders. Thus there has been a long-felt need to achieve high performance in cooling both engine coolant and charge air, while observing strict limitations in charge air pressure drop and frontal area of a radiator/charge air cooler heat exchanger package.